Ionic hydration by neutron scattering

Enderby, J. E.

doi:10.1351/pac198557081025

Cited by 15 publications

(7 citation statements)

References 7 publications

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“…Earlier neutron scattering data report hydration numbers of 7.0 ± 0.4 (79) whilst other experiments yielded values of 5.5 ± 0.4 (82). Therefore, the coordination numbers for bulk electrolyte predicted in this study from the ECC simulations are consistent with previous theoretical and experimental data.…”

Section: Ion Hydration Within the Nanoporesupporting

confidence: 89%

Influence of effective polarization on ion and water interactions within a biomimetic nanopore

Phan

Lynch

Crain

et al. 2021

Preprint

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Interactions between ions and water at hydrophobic interfaces within ion channels and nanopores are suggested to play a key role in the movement of ions across biological membranes. Previous molecular dynamics (MD) simulations have shown that the affinity of polarizable anions to aqueous/hydrophobic interfaces can be markedly influenced by including polarization effects through an electronic continuum correction (ECC). Here, we designed a model biomimetic nanopore to imitate the polar pore openings and hydrophobic gating regions found in pentameric ligand-gated ion channels. MD simulations were then performed using both a non-polarizable force field and the ECC method to investigate the behavior of water, Na+ and Cl- ions confined within the hydrophobic region of the nanopore. Number density distributions revealed preferential Cl- adsorption to the hydrophobic pore walls, with this interfacial layer largely devoid of Na+. Free energy profiles for Na+ and Cl- permeating the pore also display an energy barrier reduction associated with the localization of Cl- to this hydrophobic interface, and the hydration number profiles reflect a corresponding reduction in the first hydration shell of Cl-. Crucially, these ion effects were only observed through inclusion of effective polarization which therefore suggests that polarizability may be essential for an accurate description for the behavior of ions and water within hydrophobic nanoscale pores, especially those that conduct Cl-.

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Section: Ion Hydration Within the Nanoporesupporting

confidence: 89%

Influence of effective polarization on ion and water interactions within a biomimetic nanopore

Phan

Lynch

Crain

et al. 2021

Preprint

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“…The left panel data show a higher and narrower first peak for Na + −O than for K + −O pair densities, indicating clearly that water oxygen coordinates much more strongly to Na + than to K + ions. This result is expected given the bulk aqueous solution structural data for the two ions. ,− What is surprising is the impact of the differences in counterion size on water−headgroup pair correlations. The right panel of Figure shows that there is a substantial decrease in the height of the first peak in the headgroup−H pair densities in K + relative to Na + RMs.…”

Section: Resultsmentioning

confidence: 73%

Molecular Dynamics Simulations of the Interior of Aqueous Reverse Micelles: A Comparison between Sodium and Potassium Counterions

2003

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We present the results of a molecular dynamics simulation study of the effects of counterion type on the properties of the interior region of aqueous reverse micelles. The model systems, which treat only the interior region at the atomistic level, are designed to represent water-in-oil microemulsions formed by the aerosol-OT surfactant, either with its usual counterion, Na + , or with the K + counterion. Our study covers the water content, w0 ) [H2O]/[surfactant], range of 1-7.5, where the reverse micelles are approximately spherical and contain tens to hundreds of water molecules in their interior pool. We find that several key structural and dynamical features of the reverse micelle water pool are strongly affected by counterion type. These effects can be ascribed to the differences in headgroup-counterion coordination and to the stronger affinity for water that the smaller Na + ion exhibits. At low water content, K + ions are able to coordinate four headgroups, while Na + coordinates a maximum of three. As w0 increases, this coordination number decreases for both ions but always remains higher for K + , which also has a stronger tendency to remain in the interfacial region than does Na + . K + displaces water from the interface to a larger extent than does Na + , with the result that fewer water molecules are trapped between the headgroups. That and the fact that K + has a weaker attraction for water than does Na + lead to higher mobility of water throughout the reverse micelle interior and more bulklike structural features, such as the number of water-water hydrogen bonds, in the interfacial region.

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“…LiCl, LiBr and Lil are very hygroscopic and form highly concentrated aqueous solutions, which are easily supercooled and vitrified. At ambient temperature, many investigations on these solutions have been performed using X-ray [1 -7] and neutron [8][9][10][11][12][13][14][15][16] diffraction, and computer simulation [17][18][19][20] methods. These investigations have revealed that (i) the distances of Li + -0 and Li + -H(D) are 2.0 and 2.6 Ä, respectively, with hydration numbers of four to six, depending on the salt concentration, (ii) that the coordination geometry of the water molecules in the first hydration shell of Li + is nearly tetrahedral in highly concentrated solutions, (iii) the distance X~-0(H 2 0) is 3.1, 3.3, and 3.6 Ä for CP, Br", and I -, respectively, with hydration numbers of about six, (iv) water molecules approach Li + with their dipole axis, while the X -ion with their O-H bond axis.…”

Section: Introductionmentioning

confidence: 99%

X-ray Diffraction Studies on Supercooled Aqueous Lithium Bromide and Lithium Iodide Solutions

Takamuku

Yamagami

Wakita

et al. 1997

Zeitschrift Für Naturforschung A

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X-ray diffraction measurements were performed on liquid LiBr • 5H 2 0 and Lil • 5H 2 0 at temperatures from -30 to 25 °C. The total radial distribution functions did show that on supercooling the hydration shell of the halide ions becomes more structured, while that of the lithium ions becomes distorted. The larger the halide ion, the stronger becomes the water-water interaction around halide ions with lowering temperature. However, the distance between the water molecules in the hydration shells of the halide ions depends little on their size. On the basis of the present results, together with those of our previous investigation on LiCl • 5H 2 0 at temperatures from -135 to 100°C, the effects of temperature and the size of the halide ions on the structure of the solution are discussed.

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Ionic hydration by neutron scattering

Abstract: The method of differences applied to neutron diffraction data obtained from isotopically different aqueous solutions is described. It is shown that the method allows a detailed description of ionic hydration to be given. Several examples of the technique are discussed.

Cited by 15 publications

References 7 publications

Influence of effective polarization on ion and water interactions within a biomimetic nanopore

Influence of effective polarization on ion and water interactions within a biomimetic nanopore

Molecular Dynamics Simulations of the Interior of Aqueous Reverse Micelles: A Comparison between Sodium and Potassium Counterions

X-ray Diffraction Studies on Supercooled Aqueous Lithium Bromide and Lithium Iodide Solutions

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